1. Field of the Invention
This invention relates to sonobuoy arrays and in particular to sonobuoy arrays having a global positioning system (GPS) receiver in each sonobuoy for determining the true position of the sonobuoys in the array.
2. Description of the Related Art
Sonobuoy array, or field, consisting of a plurality of individual sonobuoys are dropped in the open ocean in patterns typically numbering from about 20 to 32 sonobuoys from either aircraft or ships. Upon reaching the water, each sonobuoy floats on the surface, lowers a hydrophone to a predetermined depth, and broadcasts its hydrophone output, each on a separate frequency, to a remotely located receiver on the dispensing vehicle. These are called passive sonobuoys. The receiving vehicle simultaneously receives the transmission of all the sonobuoys in the array and produces a plot showing which sonobuoy hydrophones are producing strong acoustic responses and which hydrophones are producing weak responses. Utilizing this plot, an analysis can locate the submerged source of the sound.
Initially the sonobuoys are placed in the ocean at equal intervals along a straight line, technically, a segment of a geodesic. After a time lapse of minutes to a few hours after the sonobuoys are placed in the ocean, the sonobuoys drift from their original positions along the straight line as the result of wind, ocean currents, and sea state. As a result, the sonobuoys no longer form a well-defined pattern in the water. The acoustic signals they broadcast become difficult to correctly interpret because of the dispersion of the individual sonobuoys makes it difficult to properly position the location of the underwater sound source. Even though the sonobuoys may still have battery power and not yet have reached the time for self-destruction, the array has reached the end of its useful life for the accurate detection and location of acoustic sound sources.